discovery: add new option to toggle gossip rate limiting

In this commit, we add a new option to toggle gossip rate limiting. This
new option can be useful in contexts that require near instant
propagation of gossip messages like integration tests.

server.go

@@ -804,6 +804,7 @@ func newServer(cfg *Config, listenAddrs []net.Addr,
 		MinimumBatchSize:        10,
 		SubBatchDelay:           time.Second * 5,
 		IgnoreHistoricalFilters: cfg.IgnoreHistoricalGossipFilters,
+		GossipUpdateThrottle:    !cfg.ProtocolOptions.NoGossipThrottle(),
 	},
 		s.identityECDH.PubKey(),
 	)